Method of cold working hollow headed articles



Jan. T, 1946. JOHNSON 2,392,152

METHOD OF COLD WORKING HOLLOW HEADED ARTICLES Filed Jan. 24, 1942 /5 A? Ame ea a. a i, w ite Patti R Johnson, Willoughhy, @lno, assignor to ihornpson Products, inc, a corporation oi. @hlo Application January as, 1M2, Serial No. scales 4 Claims.

This invention relates to the strengthening of the heads of hollow headed articles such a poppet valves.

More specifically the invention relates to the cold working of hollow arched or domed poppet valve heads to increase the hardness, strength and elastic limits thereof.

Increasingly heavy duty in aircraft engines has To overcome this deficiency the valve heads have been made with thicker dome walls. However, the increase in thickness of a valve wall is objectionable because it increases the weight of the valve and decreases the cooling rate thereby causing the valve head to assume higher temperatures in operation. As the valve increases in temperature it tendency to warp and distort increases so that the solution of the collapsing problem by way of thicker dome walls for the valve is not satisfactory.

According to the present invention hollow arched or domed poppet valve heads are cold worked to increase their strength so as to enable them to resist collapsing forces even when they are subjected to the very severe operating conditions in high speed, high compression aircraft engines, without, however, increasing the weights of the valves.

According to this invention a hollow headed caused collapse of the domes of hollow head valves.

concave segmental spherical pressing surface with r a longer radius than that of the dome of the blank is then forced against the dome so as to deform it. The partial collapse of the dome into conformity with the curvature of the pressing suriace cold works the valve metal. Since the die will not permit spreading of the head all of the stresses in the head will be around the dome and, as a resuit, the hollow cavity in the valve is not destrayed. If desired the diameter of the punch can be slightly less than the diameter of the valve head to provide an exposed marginal area around the dome of the valve wherein the valve metal can now. This permits the dashing of the metal around the punch and prevents excessive die stresses.

Since the valve blanks are usually made of austenitic steel the cold working operationcan be carried out below the recrystallization temperature of the steel thereby causing a permanent deformation of the components of the aggregates in the steel which may be composed of cementite and austenite. This permanent deformation is effected by distorting the existing structure in the steel chiefly through the stretching or elongation of the crystalline elements in the direction of the applied stresses. Actually, the distortion or straining of the metal does not result in a distortion of the crystals but rather involves a yielding of the crystals through successive crystalline slip planes. The cold worked metal has an increased tensile strength, elastic limit, and hardness.

If the valve head is to be provided with a hard seat such as a Stellite seat, the Stellite material can be puddled or welded into a groove in the blank before the cold working operation so that, after the cold working operation, the blank need not again be heated to forging temperatures which might destroy the cold worked properties of the valve head.

It is, then, an object of the invention to increase the strength of hollow headed articles without increasing the weight of the articles or the thickness of the article walls. I A further object of th invention is to provide a process of cold working the domed or -arched heads of hollow headed articles to improve the metallurgical characteristics of the articles 'A still further object of the invention is to partially collapse arched or domed heads of hollowarticles to improve the characteristics of the heads.

A still further object of the invention is to cold work the heads of hollow headed poppet valves through a partial collapse of the headarches or domes.

Another object of the invention is to reshape the arches of hollowfjheaded poppet valves through a pressure deformation treatment and thereby cold V work the heads.-

Other and'further obiects of the invention Willi be apparenttetnose skilled in the art from the following "netsiiedjdescription of the annexed hichby'way of a preferred example illustrates one embodiment of the invent,

tion.

On the drawing: Figure 1 is a plan view of a metal billet from the process of preparing a hollow valve from the billet.

Figure 4 is a vertical cross-sectional view of a valve blank formed from the blank of Figure 3.

Figure 5 is a vertical cross-sectional view, with parts in elevation, illustrating the manner in which the blank of Figure 4 is subjected to the cold working operation according to this invention.

Figure 6 is a view similar to Figure 5 but illustrating the form of the valve blank upon completion of the cold working treatment.

As shown on the drawing:

In Figures 1 and 2 the reference numeral Ill designates 'a solid cylindrical metal billet or slug preferably composed of a steel suitable for a poppet valve such as, for example, an austenitic steel. v

A nickel-chromium alloy a-ustenitic steel resistant to corrosion is highly desirable. A steel of this type having very desirable properties for hollow valves is one having the following formula:

Per cent Ni 14 Cr 14 W 2.5 C 0.35 Fe Remainder The billet i0 is heated to a forging temperature and die pressed over a central stake to form the thimble-shaped blank ll of Figure 3. The thimble-shaped blank has a domed or arched head Ila and a hollow shank or body portion llb. The blank II from the die pressing operation is reamed out to provide a cylindrical cavity llc closed by the head Ila and having an enlarged inner end lid which can be formed by an undercutting tool.

The blank H is then further forged by means of peening hammers to neck down the shank portion llb adjacent the head Ila as more fully described in the McBride et al. Patent 1,984,751,

dated December 18. 1934. After the shank has been necked down the blank is further die pressed through an extruding die as also described in the referred to McBride et al. patent to produce the valve blank 12 of Figure 4. This valve blank I! has a domed or arched hollow head Ila, a hollow head cavity I21) and a collapsed solid valve stem I20 with a nubbin end I2d.v The neck of the valve between the head He and stem He can be machined to provide a groove i3 for receiving a seating ring it (Figures 5 and 6) therein.- The seating ring can be composedof a hard alloy such as Stellite and can be puddled into the groove iii.

The blank Me with the seat ll therein is next mounted in a split die l5 as shown in Figures 5 and 6. The die l5 snugly receives the neck of the valve, at least a portion of the valve stem lie and confines the entire periphery of the head He. In other words the die I5 is formed with a shoulder l5a snugly seating the side wall of the head I21: and a converging seat l5b snugly receiving the neck of the valve.

As best shown in Figure 5, the outer top surface of the head In of the blank I! is a segment of a sphere having a relatively short radius R centered in the axial center of the stem lie just adjacent the neck portion of the blank. The head In is thus domed or arched to a considerable extent, which is more than that desired in the finished valve.

The cavity I2b of the blank has the head wall surface thereof strucl; from an even shorter radius R1 centered in the cavity as shown in Figure 5. As a result, the dome-defining wall of the head Fla is somewhat thinner at the axial center thereof than at the outer ends thereof. The shape of the dome-defining wall is controlled by the shape of the dies and reaming tools used in forming the blank.-

When the blank I2 is at a temperature below 1 the recrystallization range of the steel from which it is made, a punch it having a concave pressing face lGa is brought down on top of the valve head l2a, The face lSa of the punch I has a segmental spherical depression struck from a radius R2 which is longer than the radii R and R1 of the valve dome wall. As a result, the pressing face is flatter than the dome wall and will effect a'partial collapsing of the wall as shown in Figure 6. Since the die it confines the valve head l2a against spreading, the dome or arch of the valve head will be flattened without destroying the cavity I2b. During the pressure treatment the valve head I20 is therefore deformed and cold worked since the punch will flatten out the arched or domed wall of the'valve head and, in so doing, will cause a yielding of the crystalline elements in the steel of the head through successive crystalline slip planes therebygiving thehead cold worked metallurgical properties. The deformation of the head effected by the punch will somewhat thicken the dome wall at the center thereof as indicated in Figure 6 so that it has substantially uniform. thickness across its span.

40 pressure treatment are around a sphere and spherical distance from side wall to side wall of the valve head has decreased with a resulting increase in thickness of the head. The increase in thickness is greatest at the center. v

The punch I6 is preferably of smaller diameter than the diameter of the head He so as to expose a marginal area ll of the valve head as shown in Figure 6. This will permit the formation of a small flash of metal which can bulge up around the punch. The formation-of such a flash reif desired, be given a lowtemperature draw at 300 to 500 F. to restore 'its elastic limit. Such a treatment will not destroy the benefits of the cold working, As a result, the cold worked metallurgical properties of the head are maintained and the valve will have a much stronger head.

The punch I6 is made with a larger spherical radius R: than that of the head of the valve blank, but this radius R: corresponds to the radius desired for the dome of the finished valve.

Thus considerable cold working of the valve head All of the forces during the.

valve head, during the pressure treatment, is confined so that it cannot spread, The confining die forms a sumcient seat for the valve blank so that the blank will not be extruded during the pressure treatment.

It will, of course, be understood that various details of the method may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. A method of strengthening the heads of hol- 1 low headed austenitic steel poppet valves which crystallization range, and pressing against the dome of the confined head a spherically concave surface of longer radius than the radius of the dome of the head to partially collapse the dome into the desired contour while simultaneously thickening the metal defining the dome.

2. In the method of strengthening the domed heads of hollow headed poppet valves the steps which comprise confining against radial spreading the neck portion and hollow head or a valve blank having internally unsupported head me of shorter dius than desired in the iin ed valve, pres a concave surface against the dome of the hollow head of the confined valve to partially flatten said dome. and exposing a marginal area of the valve head during said pressing treatment to permit the formation of a metal flash around the valve head.

3. A method of strengthening the heads of hollow headed austenitic steel poppet valves. which includes the steps or forming the pop et valve with a hollow head having an external curvate surface of shorter radius than desired in the finished valve, confining the lnternallyunsupported hollow head against lateral spreading,

maintaining the steel of the valve below its recrystallization range, and pressing against the curved surface oi the head another curvate surface of greater radius to reform the valve head into the desired contour while simultaneously thickening the metal in the upper portion of the hollow head.

d. In the method of strengthening the heads of hollow headed poppet valves, the steps of confining against radial expansion the neck portion and hollow head or a valve blank having an internally unsupported head having a generally arched top of shorter radius than desiredin the finished valve, pressing another surface having a shape complemental to the desired shape of the finished valve against the hollow head to reshape the same, and exposing a marginal area oi the valve head during said pressing treatment to permit the iormation or a metal ilaeh around the valve head.

PA I. JOHNBOW. 

